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Taboni A, Fagoni N, Fontolliet T, Vinetti G, Ferretti G. Baroreflex dynamics during the rest to exercise transient in acute normobaric hypoxia in humans. Eur J Appl Physiol 2024:10.1007/s00421-024-05485-4. [PMID: 38656378 DOI: 10.1007/s00421-024-05485-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Accepted: 03/26/2024] [Indexed: 04/26/2024]
Abstract
PURPOSE We hypothesised that during a rest-to-exercise transient in hypoxia (H), compared to normoxia (N), (i) the initial baroreflex sensitivity (BRS) decrease would be slower and (ii) the fast heart rate (HR) and cardiac output (CO) response would have smaller amplitude (A1) due to lower vagal activity in H than N. METHODS Ten participants performed three rest-to-50 W exercise transients on a cycle-ergometer in N (ambient air) and three in H (inspired fraction of O2 = 0.11). R-to-R interval (RRi, by electrocardiography) and blood pressure profile (by photo-plethysmography) were recorded non-invasively. Analysis of the latter provided mean arterial pressure (MAP) and stroke volume (SV). CO = HR·SV. BRS was calculated by modified sequence method. RESULTS Upon exercise onset in N, MAP fell to a minimum (MAPmin) then recovered. BRS decreased immediately from 14.7 ± 3.6 at rest to 7.0 ± 3.0 ms mmHg-1 at 50 W (p < 0.01). The first BRS sequence detected at 50 W was 8.9 ± 4.8 ms mmHg-1 (p < 0.05 vs. rest). In H, MAP showed several oscillations until reaching a new steady state. BRS decreased rapidly from 10.6 ± 2.8 at rest to 2.9 ± 1.5 ms mmHg-1 at 50 W (p < 0.01), as the first BRS sequence at 50 W was 5.8 ± 2.6 ms mmHg-1 (p < 0.01 vs. rest). CO-A1 was 2.96 ± 1.51 and 2.31 ± 0.94 l min-1 in N and H, respectively (p = 0.06). HR-A1 was 7.7 ± 4.6 and 7.1 ± 5.9 min-1 in N and H, respectively (p = 0.81). CONCLUSION The immediate BRS decrease in H, coupled with similar rapid HR and CO responses, is compatible with a withdrawal of residual vagal activity in H associated with increased sympathetic drive.
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Affiliation(s)
- Anna Taboni
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, Brescia, Italy.
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.
| | - Nazzareno Fagoni
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, Brescia, Italy
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Timothée Fontolliet
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Giovanni Vinetti
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, Brescia, Italy
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Guido Ferretti
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, Brescia, Italy
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
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Taboni A, Fagoni N, Fontolliet T, Vinetti G, Ferretti G. Dynamics of cardiovascular and baroreflex readjustments during a light-to-moderate exercise transient in humans. Eur J Appl Physiol 2022; 122:2343-2354. [PMID: 35861802 PMCID: PMC9561001 DOI: 10.1007/s00421-022-05011-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 07/07/2022] [Indexed: 12/02/2022]
Abstract
Purpose We hypothesised that, during a light-to-moderate exercise transient, compared to an equivalent rest-to-exercise transient, (1) a further baroreflex sensitivity (BRS) decrease would be slower, (2) no rapid heart rate (HR) response would occur, and (3) the rapid cardiac output (CO) response would have a smaller amplitude (A1). Hence, we analysed the dynamics of arterial baroreflexes and the HR and CO kinetics during rest-to-50 W (0–50 W) and 50-to-100 W (50–100 W) exercise transients. Methods 10 subjects performed three 0–50 W and three 50–100 W on a cycle ergometer. We recorded arterial blood pressure profiles (photo-plethysmography) and R-to-R interval (RRi, electrocardiography). The former were analysed to obtain beat-by-beat mean arterial pressure (MAP) and stroke volume (SV). CO was calculated as SV times HR. BRS was measured by modified sequence method. Results During 0–50 W, MAP transiently fell (− 9.0 ± 5.7 mmHg, p < 0.01) and BRS passed from 15.0 ± 3.7 at rest to 7.3 ± 2.4 ms mmHg−1 at 50 W (p < 0.01) promptly (first BRS sequence: 8.1 ± 4.6 ms mmHg−1, p < 0.01 vs. rest). During 50–100 W, MAP did not fall and BRS passed from 7.2 ± 2.6 at 50 W to 3.3 ± 1.3 ms mmHg−1 at 100 W (p < 0.01) slowly (first BRS sequence: 5.3 ± 3.1 ms mmHg−1, p = 0.07 vs. 50 W). A1 for HR was 9.2 ± 6.0 and 6.0 ± 4.5 min−1 in 0–50 W and 50–100 W, respectively (p = 0.19). The corresponding A1 for CO were 2.80 ± 1.54 and 0.91 ± 0.55 l∙min−1 (p < 0.01). Conclusion During 50–100 W, with respect to 0–50 W, BRS decreased more slowly, in absence of a prompt pressure decrease. BRS decrease and rapid HR response in 50–100 W were unexpected and ascribed to possible persistence of some vagal tone at 50 W. Supplementary Information The online version contains supplementary material available at 10.1007/s00421-022-05011-4.
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Affiliation(s)
- Anna Taboni
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Nazzareno Fagoni
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.,Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.,AAT Brescia, Department of Anaesthesiology, Intensive Care and Emergency Medicine, Spedali Civili University Hospital, Brescia, Italy
| | - Timothée Fontolliet
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Giovanni Vinetti
- Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy. .,Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.
| | - Guido Ferretti
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.,Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy
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Ferretti G, Fagoni N, Taboni A, Vinetti G, di Prampero PE. A century of exercise physiology: key concepts on coupling respiratory oxygen flow to muscle energy demand during exercise. Eur J Appl Physiol 2022; 122:1317-1365. [PMID: 35217911 PMCID: PMC9132876 DOI: 10.1007/s00421-022-04901-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Accepted: 01/25/2022] [Indexed: 12/26/2022]
Abstract
After a short historical account, and a discussion of Hill and Meyerhof's theory of the energetics of muscular exercise, we analyse steady-state rest and exercise as the condition wherein coupling of respiration to metabolism is most perfect. The quantitative relationships show that the homeostatic equilibrium, centred around arterial pH of 7.4 and arterial carbon dioxide partial pressure of 40 mmHg, is attained when the ratio of alveolar ventilation to carbon dioxide flow ([Formula: see text]) is - 21.6. Several combinations, exploited during exercise, of pertinent respiratory variables are compatible with this equilibrium, allowing adjustment of oxygen flow to oxygen demand without its alteration. During exercise transients, the balance is broken, but the coupling of respiration to metabolism is preserved when, as during moderate exercise, the respiratory system responds faster than the metabolic pathways. At higher exercise intensities, early blood lactate accumulation suggests that the coupling of respiration to metabolism is transiently broken, to be re-established when, at steady state, blood lactate stabilizes at higher levels than resting. In the severe exercise domain, coupling cannot be re-established, so that anaerobic lactic metabolism also contributes to sustain energy demand, lactate concentration goes up and arterial pH falls continuously. The [Formula: see text] decreases below - 21.6, because of ensuing hyperventilation, while lactate keeps being accumulated, so that exercise is rapidly interrupted. The most extreme rupture of the homeostatic equilibrium occurs during breath-holding, because oxygen flow from ambient air to mitochondria is interrupted. No coupling at all is possible between respiration and metabolism in this case.
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Affiliation(s)
- Guido Ferretti
- Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Brescia, Italy.
- Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Université de Genève, Genève, Switzerland.
| | - Nazzareno Fagoni
- Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Brescia, Italy
| | - Anna Taboni
- Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Université de Genève, Genève, Switzerland
| | - Giovanni Vinetti
- Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Brescia, Italy
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Taboni A, Fagoni N, Fontolliet T, Moia C, Vinetti G, Ferretti G. A closed-loop approach to the study of the baroreflex dynamics during posture changes at rest and at exercise in humans. Am J Physiol Regul Integr Comp Physiol 2021; 321:R960-R968. [PMID: 34643104 DOI: 10.1152/ajpregu.00167.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We hypothesized that during rapid uptilting at rest, due to vagal withdrawal, arterial baroreflex sensitivity (BRS) may decrease promptly and precede the operating point (OP) resetting, whereas different kinetics are expected during exercise steady state, due to lower vagal activity than at rest. To test this, eleven subjects were rapidly (<2 s) tilted from supine (S) to upright (U) and vice versa every 3 min, at rest and during steady-state 50 W pedaling. Mean arterial pressure (MAP) was measured by finger cuff (Portapres) and R-to-R interval (RRi) by electrocardiography. BRS was computed with the sequence method both during steady and unsteady states. At rest, BRS was 35.1 ms·mmHg-1 (SD = 17.1) in S and 16.7 ms·mmHg-1 (SD = 6.4) in U (P < 0.01), RRi was 901 ms (SD = 118) in S and 749 ms (SD = 98) in U (P < 0.01), and MAP was 76 mmHg (SD = 11) in S and 83 mmHg (SD = 8) in U (P < 0.01). During uptilt, BRS decreased promptly [first BRS sequence was 19.7 ms·mmHg-1 (SD = 5.0)] and was followed by an OP resetting (MAP increase without changes in RRi). At exercise, BRS and OP did not differ between supine and upright positions [BRS was 7.7 ms·mmHg-1 (SD = 3.0) and 7.7 ms·mmHg-1 (SD = 3.5), MAP was 85 mmHg (SD = 13) and 88 mmHg (SD = 10), and RRi was 622 ms (SD = 61) and 600 ms (SD = 70), respectively]. The results support the tested hypothesis. The prompt BRS decrease during uptilt at rest may be ascribed to a vagal withdrawal, similarly to what occurs at exercise onset. The OP resetting may be due to a slower control mechanism, possibly an increase in sympathetic activity.
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Affiliation(s)
- Anna Taboni
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland
| | - Nazzareno Fagoni
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.,Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy.,AAT Brescia, Department of Anaesthesiology, Intensive Care and Emergency Medicine, Spedali Civili University Hospital, Brescia, Italy
| | - Timothée Fontolliet
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.,Department of Basic Neurosciences, University of Geneva, Geneva, Switzerland
| | - Christian Moia
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.,Department of Basic Neurosciences, University of Geneva, Geneva, Switzerland
| | - Giovanni Vinetti
- Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy
| | - Guido Ferretti
- Department of Anaesthesiology, Pharmacology, Intensive Care, and Emergencies, University of Geneva, Geneva, Switzerland.,Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy.,Department of Basic Neurosciences, University of Geneva, Geneva, Switzerland
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Abstract
PURPOSE Water immersion adds additional drag and metabolic demand for limb movement with respect to air, but its effect on the internal metabolic power (Ėint) of cycling is unknown. We aimed at quantifying the increase in Ėint during underwater cycling with respect to dry conditions at different pedaling rates. METHODS 12 healthy subjects (4 females) pedaled on a waterproof cycle ergometer in an experimental pool that was either empty (DRY) or filled with tap water at 30.8 ± 0.6 °C (WET). Four different pedal cadences (fp) were studied (40, 50, 60 and 70 rpm) at 25, 50, 75 and 100 W. The metabolic power at steady state was measured via open circuit respirometry and Ėint was calculated as the metabolic power extrapolated for 0 W. RESULTS Ėint was significantly higher in WET than in DRY at 50, 60 and 70 rpm (81 ± 31 vs 32 ± 30 W, 167 ± 35 vs 50 ± 29 W, 311 ± 51 vs 81 ± 30 W, respectively, all p < 0.0001), but not at 40 rpm (16 ± 5 vs 11 ± 17 W, p > 0.99). Ėint increased with the third power of fp both in WET and DRY (R2 = 0.49 and 0.91, respectively). CONCLUSION Water drag increased Ėint, although limbs unloading via the Archimedes' principle and limbs shape could be potential confounding factors. A simple formula was developed to predict the increase in mechanical power in dry conditions needed to match the rate of energy expenditure during underwater cycling: 44 fp3 - 7 W, where fp is expressed in hertz.
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Affiliation(s)
- Giovanni Vinetti
- Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY Department of Anaesthesiology, Clinical Pharmacology, Intensive Care and Emergency Medicine, University of Geneva, Geneva, Switzerland
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